Working at the Naval Research Laboratory (NRL), American physicist Roger Easton was involved in development of the Vanguard, Minitrack, and Navy Space Surveillance Systems for spacecraft tracking, navigation and timing technology. He is best known for designing the US Navy's Timation (time navigation) geopositioning system, which used multiple satellites carrying stable and ultra-precise clocks to send signals allowing earth-based receiving devices to calculate their exact locations. Patented in 1974 after several years of design, construction, and collaboration, Easton's system forms the foundation for the NAVSTAR-Global Positioning System (GPS).